1. Field of the Invention
This invention relates to an integrated control system of a vehicle, more particularly to an integrated vehicle control system which integrates two kinds of controls, comprised of that to avoid an obstacle present on the course of travel ahead of the vehicle and that to ensure stability of the vehicle.
2. Description of the Related Art
Various obstacle avoidance techniques have hitherto been proposed. For example, Japanese Laid-open Patent Application Hei 6(1994)-298022 teaches detecting the distance to an obstacle (e.g., another vehicle running ahead on the road) and automatically operating a brake, if needed, so as to avoid the contact with the obstacle.
Moreover, there has been proposed a technique to control the braking forces independently or separately for the four wheels to generate a yaw moment (moment about the gravitational direction at the center of the gravity of the vehicle) so as to control the behavior or motion of the vehicle. More specifically, the technique detects the slip angle and angular velocity of the vehicle body to determine whether the vehicle tends to oversteer, while detecting the actual yaw rate (yaw angular velocity) to determine the error from a desired yaw rate to determine whether the vehicle tends to understeer.
In this technique, the front wheels or rear wheels are braked in response to the determined results to control the vehicle yaw moment, thereby ensuring stability when the vehicle corners or turns.
In the obstacle avoidance control mentioned above, the automatic brake operation may cause the vehicle driver to experience annoyance if he has the intention to avoid the obstacle by himself. For that reason, the obstacle avoidance control is configured such that the automatic braking is only effected after the possibility of contact has grown to a great extent. However, once the automatic braking is effected, it instantaneously generates large braking forces. This may sometimes cause unstable vehicle behavior.
Such an obstacle avoidance control and vehicle behavior control as mentioned above could be integrated together so as to, for example, make the vehicle behavior stable when the vehicle tends to oversteer. Since, however, the vehicle behavior control is configured to respond to the vehicle driver's manipulation, if the automatic braking yields large braking forces instantaneously, the integrated control could fail to ensure vehicle stability sufficient for avoiding an obstacle on the road.